Roller ball pen



FIG. 1 is a perspective view of a roller ball pen showing my new design;

FIG. 2 is a front elevational view;

FIG. 3 is a right side elevational view, the left said being a mirror image thereof;

FIG. 4 is a rear elevational view;

FIG. 5 is a top plan view; and,

FIG. 6 is a bottom plan view. 

The ornamental design for a roller ball pen, as shown and described. 